Apparatus for finding the direction of sound



July 9, 1929. w, WALKER 1.719.951

APPARATUS FOR FINDING THE DIRECTION OF SOUND Filed April 22, 1925 HIS ATTORNEYS.

WILLIAM L. WALKER, OF NEW YORK, N. Y., ASSIGNOR T WALKER SIGNAL & EQUIP-MENT GORPOBATION, A CORPORATIGN OF DELAWARE.

APPARATUS FOR FINDING THE DTRECTION OF SOUND.

Application filed April 22, 1925. $eria1. No. 25,011.

My invention relates to the detection of sound direction or e locationof the source of sound by measuring the difference in sound intensityfrom a given source received at two diiierent locations, and has for itsobject the provision of: a simple, compact and eificient device of thischaracter. While my invention is especially adapted for navigationalpurposes to detect the location of submarine signals and the like, it ofcourse is not limited to such use.

My invention will be fully understood from the following descriptiontaken in connection with the accompanying drawings and its scope will bepointed out in the appended claims.

In the drawings, Figure 1 is a diagramof the1 circuits and apparatus ofmy invention, an

Fig. 2 is an ,end view of the microphone switch.

Referring to the drawings in which the nu.- merals 1 and 2 indicate twomicrophones, which may be of any preferred type, positioned in spacedrelation. When my invention is used on board ship, one pair of thesemicrophones is preferably positioned near the bow of theship and,another pair near the stern ofthe ship below the water line on the portand starboard sides respectively.

The fore and aft pairs of microphones are used in identical manners andtherefore the use of one only will be described. The microphone 1 isconnected on one side to a battery 3 and on the other side with contacts4 and 5 positioned on opposite sides of a double throw switch 6.Microphone 2 is similarly connected with battery 3 and contacts 7 and 8of switch 6. The switch blades 6', 6", are preferably of segmental form,as shown in Fig. 2. These blades are of sufiici'ent width to spanrespectively the contacts 4, 7 and 5, 8, when the switch 6 is in itsneutral or middle position. The purpose of this arrangement is toshort-circuit the microphones while the switch is operated to connectone or the other of the microphones and thereby prevent a clicking soundin the telephones. For example, when the switch 6 is in the full lineposition shownin Fig. 2, in which microphone 2 is connected withcontactlO and it is desired to connect microphone 1 with contact 10, theswitch 6 is thrown vto the right as indicated in dotted lines in Fig. 2.During this movement, microphones 1 and 2 are short-circuited 9 and 10of switch 6 are connected to contacts 11 and 12 of switch13, and battery3 is connccted with contacts 14 and 15 of switch 13 as shown. The blade13 of switch 13 is similar to blades 6, 6" of switch 6, andshortcircuits the telephones while the switch 13 is operated to preventclicking sounds.

It is thereforev clear that by throwing switch 6 to one side or theother, either of the microphones may be connected with switch 13. Onswitch 13, terminal 16'is intermediate contacts 11 and 12, and terminal17 is intermediate contacts 14 and 15. The primary coil 18 of atransformer 19 is connected across' contacts '16, 17 by conductors 20,21. A choke coil 22 is in parallel, and a condenser 23 is in series withthe coil 18. A condenser 24 preferably is of the order of one microfaradand is connected with an intermediate point in the coil 18 and may beconnected thereto by switch 25. The purpose of the condenser 24 and theswitch 25 is to greatly increase the volume of sound transmitted by themicrophones 1 and 2, when the signals are weak owing to greaterdistances. I have found that a condenser of about one microfaradcapacitance has this effect over a wide range of frequencies, such asfrom to 1200 vibrations per second. Why this result is obtained, Icannot at present explain, but I have found that the volume is greatlyincreased irrespective of any question of resonance. From this itwill beseen that either of the microphones may be connected with primary coil18 by switch 13. The switch 13 is also provided with contacts 26, 27,across which the secondary coil 28 is connected by conductors 29, 30,having a condenser 31 in parallel. The coils 18 and 28 are electricallysimilar and are wound on opposite poles 32 and 32 formed on a ringshaped yoke 33. Intermediate said poles is 42 which is graduated toindicate the direction of the source of sound from a comparison of theintensities of the sound at different points and the] adjustmentnecessary to balnected with either of the coils 28, 35. It will beapparent that the coil 28 is provided as "an additional secondary forthe transformer in order to eliminate the necessity of turning thearmature coil and its pointer 41 back to zero orto the positionofmaximum effect when throwing the microphone producing the weaker signalsinto circuit. In other words, the coil 28 is used when listening to thesounds from the weaker microphone in place of the coil 35 in order tocompare the current in the coil 28 with the current produced by thereduced volume of signals as determined by the position of the coil 35,without returning the latter to zero position. It will be obvious,however, that the transformer may be used with only the coils 18 and 35if the, coil is turned to zero position each time the signals from theweaker microphone are listened to. The aft, starboard, and portmicrophones 1 and 2 may be connected with the switch 6 by means of thefour pole switch 50, in which case the said aft microphones will beconnected with the transformer and telephone circuits, and the procedurein finding direction astern is identical with that described inconnectionwith the microphones 1 and 2.

Having described the structural details of my invention, its operationwill be readily understood from the following brief description.

The switch 13 is thrown to the right to con= nect the telephone 45 withsecondary coil 28, the coil 35 now being disconnected and inactive, sothat lines of force may freely pass between the poles 32 and 32. Theoperator then operates switch ,6 to connect alternately.

microphones 1 and 2 with primary coil 18, and compares the intensitiesof the sounds of each. After having determined which of the microphonesounds the louder, the switch 6 is positioned to connect that microphonewith switch 13, which, for purposes of illus t-rat-ion is assumed to bemicrophone 1. The switch 6 is thrown to the right The switch 13 is thenthrown to the left to connect the telephone with coil 35, and this coilis manually rotated clockwise until the intensity frommicrophone 1 hasbeen reduced to that of the weaker microphone, which in the case assumedis microphone 2, in which position the pointer 41 will indicate thedirection of the source of sound as above set forth. If the operatordesires to'make further comparisonsbctween the modified signal now heardfrom the microphone 1 andthe weaker imaeei forth prior to the detaileddescription will readily be reco nized. I do not wish to be understoodas beinglimited to the details of form or arrangement of part herein setforth, for various changes may be made by those skilled in the artwithout departing from the spirit or scope of my invention.

What I claim is:

1. Appartus for finding the direction of sound comprising in combinationtwo spaced microphones, a telephone circuit, a transformer having afixed primary coil, a fixed secondary coil, said coils being on a commoncore, a movable coil positioned in the electromagnetic field of saidtransformer, said movable coil being mounted upon a core of such shapethat the reluctance of the magnetic circuit through said fixed coilsremains constant, means. for connecting the primary of said transformerwith either of the microcommon core, said variable secondary beingmounted upon a rotatable core of such shape that the reluctance of themagnetic circuit through said fixed coils remains constant, means forconnecting the microphones alternat'ely with, said primary, means forconnecting the telephone with said fixed secondary whereby the intensityof the sounds may be compared, means for connecting the telephone withsaid variable secondary whereby the inductive coupling between saidprimary coil and saidvariable secondary coil may be varied to reduce theintensity of thelouder sounding microphone to that of the othermicrophone, and means indicating the amount of variation of saidvariable sec ndary comprising a pointer movable there ith and a scalecalibrated to indicte the direction of sound sources calculated fromsound intensitie's.

3. Apparatus for finding the direction of sound comprising incombination two spaced microphones adapted to receive sound from thesame source with unequal intensity, a telephone, a transformer having afixed primary coil and a fixed secondary coil and a movable secondarycoil, said fixed coils being ona common core, said movable secondarycoil being mounted upon a core of such shape that the reluctance of themagnetic circuit through the fixed coils remains constant, means forconnecting either of the microphones with said primary and means forconnecting the telephone with said fixed secondary for the purpose ofcomparing the sound intensity of said microphones, means for connectingthe telephone with sald movable secondary whlle the louder soundingmicrophone in connected core and a secondary coil on a rotatable mem-'ber positioned intermediate said fixed primary and secondary, saidrotatable member being of such shape that the reluctance of the magneticcircuit through the fixed coils remains constant, means for connectingeither of the microphones withsaid primary, means for connecting saidtelephone with either of the secondaries, and means indicating theamount of rotation of said member.

5. Apparatus for finding the direction of sound comprising incombination two spaced microphones adapted to receive sound from thesame source with unequal intensity, a telephone, a transformer having afixed primary coil and a fixed secondary coil on the same core and asecondary coil on a movable member intermediate said fixed primary andsecondary coils, said movable member being of such shape that thereluctance of the magnetic circuit through 'the fixed coils remainsconstant, means for connecting either of the microphones with saidprimary, means for connecting the telephone with the fixed secondarywhereby the intensity of the microphones may be compared, means forconnecting the telephone with said movable secondary while the loudermicrophone is connected with the primary whereby the intensity thereofmay be reduced to that of the other microphone by movement of themovable secondary, and means indicating the direction of the soundsource comprising an indicator movable with said movable secondary and acooperating scale calibrated to indicate directions for givenintensities.

6. Apparatus for finding the direction of sound comprising, means forreceiving sound waves and converting the same into correspondinglyvarying electric currents, a transformer having a metallic core, incircuit therewith and having stationary primary and secondary coils anda secondary coil relatively rotatable thereto in inductive relation witheach other, said rotatable secondary coil being mounted upon a core ofsuch shape that the reluctance of the magnetic circuit through the fixedcoils remains constant, and means in circuit with the secondary coil ofsaid transformer for detecting the vibrations of the received sound, andin which the reduction in intensity of the induced currents may bevaried according to the angular position of said rotatable coil relativeto that giving the maximum inductive effect.

7. Apparatus for finding the direction of sound comprising, means forreceiving sound waves and converting the same into corre spondinglyvarying electric currents, a transformer in circuit therewith having acore of magnetic material, a primary coil, arelatively fixed secondarycoil on the same core and a secondary coil rotatable in respect to saidtwo coils and in inductive relation therewith, said rotatable secondarycoil being mountedupon a core of such shape that the reluctance of themagnetic circuit through the fixed coils remains constant, means fordetecting the vibrations of the received sound, and a switch forincluding either of said secondary coils in circuit with said detectingmeans.

8. A transformer for converting electric currents in accordance withsound vib 'ations received at two spaced microphones, having a core ofmagnetic material, a primary coil adapted to be connected with either ofsaid microphones and a'plurality of secondary coils, one of which ismounted on said core, while the other is mounted on a rotatable core ofsuch shape that the reluctance of the magnetic circuit through theprimary coil and the first named secondary coil remains constant,whereby a comparison of the sound intensities at said microphones isobtained by the relative movement of said rotatable coil.

Dated this 16th day of April, 1925.

WILLIAM L. WALKER.

